A 40-year-old woman, admitted to the emergency hospital after a car collision, had
multiple surgeries to repair her injuries and was placed on mechanical ventilation to
assist respiration. On day 13 she was scheduled for a transesophageal ECG, and was
given a muscle relaxant IV to facilitate the procedure. Soon afterwards the patient
suffered a cardiac arrest and CPR was performed successfully. The potassium recorded
during arrest peaked at 7.3 mEq/L. Which of the following muscle relaxant was most likely
A. Cisatracurium B. Vecuronium C. Tubocurarine D. Dantrolene E. Succinylcholine
Succinylcholine-learning objective: describe the adverse effects of succinylcholine.answer: esuccinylcholine can release rapidly potassium from intracellular sites. in a normal patient thisresults in a small, transient hyperkalemia. in patients with extensive soft-tissue trauma or burns,cerebral vascular accident and prolonged stays in an intensive care unit, this hyperkalemia canbe much more pronounced when succinylcholine is given at least several days after theunderlying condition has become established. the hyperkalemia can be life threatening since itcan lead to cardiac arrest like in the present case. the cause of succinylcholine-inducedhyperkalemia in these patients seems related to up regulation of nm receptors in the skeletalmuscle. patients with the aforementioned conditions are deprived of neural influence or activitybecause of the prolonged immobilization. such deprivation stimulates the synthesis of new nmreceptors across the muscle membrane. when these receptors are activated by succinylcholinean action potential occurs, ion channels open allowing na+ to flow inside and k+ to flow outsideof the cell. since succinylcholine is metabolized more slowly than acetylcholine the receptoractivation is more prolonged, causing a larger influx of na+ and a vigorous efflux of k+. whennm receptors are increased in skeletal muscle this k+ efflux can cause a life-threateninghyperkalemia.a, b, c) nondepolarizing neuromuscular blockers cause blockade, not activation, of nmreceptors. therefore they do not induce hyperkalemia.d) dantrolene has no effect on nm receptors.